Method for producing a compression connection

ABSTRACT

A method for producing a compression connection for a driving part ( 1 ), in particular for an essentially ring-shaped driving part ( 1 ) on a shaft ( 3 ), in particular in the case of a built-up camshaft with which
         the driving part ( 1 ) has an opening that essentially corresponds to the outside diameter of the shaft ( 3 ),   the driving part ( 1 ) sits on the shaft with coverage in the finished compression connection,   an adhesive layer is applied between the circumferential surfaces of the driving part ( 1 ) and the shaft ( 3 ), is to be improved.       

     To this end, such a method is characterized by the following features:
         the driving part ( 1 ) is heated until reaching the joining temperature and is thereby widened,   the driving part ( 1 ) is pushed on to the shaft essentially without any forces.

The present invention relates to a method for producing a compressionconnection for a driving part (e.g., cams, plugs, chain wheels, phaseadjuster, bearings, . . . ), in particular for an essentiallyring-shaped driving part on a shaft, in particular with a built-upcamshaft according to the preamble of Claim 1.

For many years, casting was the dominant production technology forcamshafts for passage vehicle engines. For many years, however, therehave increasingly been camshafts of the built-up type of technology,whereby both technologies have their specific properties and advantagesas well as preferred areas of use. For camshafts produced by the castingmethod, grey cast iron, for example, is considered as the startingmaterial, but chilled cast iron is by far the most popular material forpassenger vehicle engines. For the designs of built-up camshaftsavailable on the market, there are various manufacturing technologies(MTZ volume 57, no. 5, May 1, 1996, pages 284-291). These built-upcamshafts consist essentially of a pipe (solid or hollow rod) on whichthe driving parts are mounted by different methods. Among others,joining methods are described in which conversion layers are appliedbetween the driving part and the shaft, and the joining can be performedby longitudinal or transverse compression connections, whereby thetransverse compression connection is found to be a disadvantage withrespect to the complexity of innovative equipment and the manufacturingtolerances that are difficult to maintain.

German Patent DE 197 03 260 describes a built-up crankshaft in which thecams and optionally also other add-on parts are connected to a shaftcoated with a conversion layer via a longitudinal compressionconnection. This conversion layer may be designed as an adhesive layer.In this process, the cam is joined to a shaft cold and with a largecoverage and thereby joined with high axial and radial forces. Thedisadvantage of this method is that due to the great coverage, greatplastic deformations and stresses and therefore cracks are introducedinto the system, which can no longer withstand the stresses in the valvedrive. When the conversion layer is embodied as an adhesive layer, thereis the additional disadvantage that the adhesive is displaced by thecam, which is joined with a great coverage and therefore the effect ofthe adhesive is lost entirely or at least has an extremely minor effect.Due to the minor adhesive effect to this extent, the high transferabletorques required of future valve drives cannot be achieved adequately.Another disadvantage of this longitudinal compression method that shouldbe mentioned here is that the shaft must be remachined at the bearingpoints in a complex operation after the joining process.

The present invention relates to the problem of providing an improvedembodiment of a method for producing a compression connection for adriving part on a shaft, in particular in a built-up camshaft.

This problem is solved in a generic method according to this inventionby the characterizing features of Claim 1.

This embodiment is characterized in that the driving part to be joinedto the shaft by an addition of compression seating and adhesive seatingis heated before being joined to the shaft and is therefore expanded andis thus characterized on the whole as a method involving no force, i.e.,a joining method without coverage and thus avoiding plastic deformationsand stresses and therefore cracks. Due to the joining method withoutforce in which the driving part is pushed onto the shaft withpractically no friction, the adhesive applied to the circumferentialsurfaces of the cam and/or the shaft is preserved without scraping anyoff, so that an optimal adhesive connection can be achieved. On thewhole, this method yields an especially stable connection with which thecost and weight can be minimized while maintaining the same torques andtherefore the energy expended at the required highest torques of a valvedrive is lower on the whole, so this yields a connection that isespecially secure under stress. Due to the application of adhesive, thehydrostatic pressure within the connection is increased on the one handwhile on the other hand the connecting surface is increased due to thefact that the peaks in the surface roughness is filled out within theconnection.

This yields on the whole an especially high strength of the connection,in particular a high shearing strength and therefore very hightransferable torques. Measurements have shown that connections createdby combining compression seating and adhesive seating can withstand atorque at least one-third higher.

Therefore, materials having low specifications, i.e., materials with arelatively low strength, can be used for the shaft while retaining thestrength of the connection, or a low total use of material is possiblewith the same material; this has a positive effect on unit costs on thewhole as well as the total weight of the shaft. Another great advantagein terms of unit costs is the fact that the energy required for thejoining operation is kept low on the whole because small joining lengthsand lower joining temperatures are possible, while at the same timeachieving a connection having a high stability. In addition, this methoddoes not require complex reworking of the shaft after the joiningoperation, so this also has a positive effect on unit costs and thetotal energy.

The driving agent is expediently heated by induction, hot air orradiation. Modern induction heating in particular can introduce energyinto the driving part that is to be heated in a targeted manner, so thatit can be heated to conform to demands. Induction heating generates analternating magnetic field, which in turn induces an alternating currentin the electrically conducting driving part. Because of the electricresistance of the driving part, this current induced in the driving partcauses heating of same at the sites of where currents. With suchinduction heating, it is thus possible to introduce heat specifically atcertain predefined locations through the shape of the inductor and/or byregulating the frequency used, so that heat is generated immediately anddirectly in the driving part itself, i.e., in its interior, and need notbe conducted by thermal conduction, as is the case with a traditionaloven which heats from the outside to the inside.

All the driving parts to be mounted on the shaft can be completelymachined in advance so that no remachining of the driving parts andshaft is necessary after they are mounted on the shaft.

It is self-evident that the features mentioned above and those yet to beexplained below may be used not only in the particular combination givenbut also in other combinations or alone without going beyond the scopeof the present invention.

Preferred exemplary embodiments of the invention are shown in thedrawings and explained in greater detail in the following description.

The figures show schematically:

FIG. 1 a schematic diagram of a driving part,

FIG. 2 multiple driving parts mounted on a shaft by the method accordingto the invention.

FIG. 1 shows a driving part 1, in particular a cam, having anessentially ring-shaped design equipped with a bulge 2. In addition, thedriving part 1 has an opening 4 whose diameter corresponds essentiallyto the outside diameter of the shaft 3 shown in FIG. 2. To allow thedriving part 1 to be arranged on the shaft 3 in a fixed manner, it isheated to create a compression connection by the inventive method untilreaching a joining temperature, so that the diameter d of the opening 4is increased. The widening of the diameter d of the opening 4 may beonly large enough to allow the driving part 1 in the heated state to bepushed onto the shaft 3 directly without exerting any axial or radialforces and it solidifies on reaching a predetermined position and thenis joined fixedly to the shaft 3. The application of the driving part 1is thus limited according to this invention to the extent that theadhesive applied to the connection of the driving part 1 and/or theshaft 3 is not removed at all or not to any considerable extent in thejoining operation.

1. A method for producing a compression connection for a driving part(1), in particular for an essentially ring-shaped driving part (1) on ashaft (3), in particular in the case of a built-on camshaft, wherein thedriving part (1) has an opening corresponding essentially to the outsidediameter of the shaft (3), the driving part (1) sits on the shaft withcoverage in the finished compression connection, an adhesive layer isprovided between the circumferential surfaces of the driving part (1)and the shaft (3), wherein the driving part (1) is heated until reachingthe joining temperature and is thereby widened, and the driving part (1)is pushed onto the shaft in an essentially force-free operation.
 2. Themethod according to claim 1, wherein the shaft (3) is joined withoutafter-working.